Installation & Sizing Guide

Getting a clean, snug fit starts with knowing your post — not guessing at it. This guide walks you through measuring your fence post and installing your My Post Cap in about five minutes, no tools required for most setups.

Now available in 4x4, 5x5, and 6x6 sizes — every design in our collection can be ordered in the size that matches your post, right from the size dropdown on each product page.

Step 1: Measure Your Post

Fence posts aren't always what the name suggests. A "4x4" post can actually measure anywhere from 3.5" to 4" depending on how it was milled. Here's how to tell which one you have:

• 4x4 Nominal (Actual size 3.5" x 3.5"): This is the standard pressure-treated lumber you'll find at big-box hardware stores. If your post was bought off the shelf and never resized, this is almost always your match.
• 4x4 True / Vinyl (Actual size 4.0" x 4.0"): Rough-sawn timber, cedar, or 4" vinyl post sleeves are usually cut to their full stated dimension. If your post feels noticeably thicker than standard lumber, or you're capping a vinyl sleeve, this is your match.
• 5x5 Nominal (Actual size 4.5" x 4.5"): The step up from a standard 4x4, common on larger deck and privacy fence posts bought as dressed lumber.
• 5x5 True / Vinyl (Actual size 5.0" x 5.0"): Rough-sawn or vinyl-sleeved posts sized to a full 5 inches.
• 6x6 Nominal (Actual size 5.5" x 5.5"): Standard dressed lumber for heavy-duty deck and structural posts.
• 6x6 True / Timber (Actual size 6.0" x 6.0"): Rough-sawn timber posts cut to a full 6 inches, common on gate posts and larger structural builds.

Each design's product page has all six sizes available in the size dropdown, each offered as a Single or a Set of 2.

How to measure correctly: Remove any old cap, measure across the bare top of the post at its flat edges, and always go by your actual measurement — not the size printed on the lumber label at the store. Allow about 1/16" to 1/8" of clearance for an easy, non-binding fit. If you're unsure, send us your measurement before ordering and we'll help you get it right — we can also make custom sizes on request.

Step 2: Choose Single or Set of 2

Capping a single post, like a mailbox post or a standalone corner? Go with a Single. Framing an entryway, gate, or matching pair of corner posts? The Set of 2 gives you a cohesive look and ships with free shipping.

Step 3: Install Your Cap

1. Clean the post top. Wipe away dust, debris, or old caulk so the cap can slide on cleanly.
2. Slide the cap into place. Our caps are precision crafted for a snug, friction-fit — simply slide the cap down over the top of your post until it sits flush.
3. Secure it (optional but recommended). Every cap includes a small screw hole at the rear of the base. For permanent mounting or extra wind resistance, drive one exterior-rated screw through this hole into the post.
4. Step back and admire it. That's it — your fence just got a lot more personality.

Built for the Outdoors

Every My Post Cap is made from UV-resistant PETG filament, chosen specifically to handle sun, rain, and temperature swings without yellowing, warping, or becoming brittle. Each piece is hand-inspected in our barn studio before it ships, so what you install is what you saw in the photos.

Frequently Asked Questions

What if my post is an unusual size?
Message us before you order — we're happy to help you figure out the right fit, and can sometimes accommodate custom sizing.

Do I need special tools to install?
No. The slide-on fit requires no tools at all. A screwdriver or drill is only needed if you choose to secure the cap permanently.

Will the cap fit a wobbly or slightly warped post?
Our caps are designed for a snug fit on standard dimensions, but posts that have significantly warped or splayed at the top may need light sanding for the cleanest fit.

Browse the full collection →